August 6, 2013
Subaru Telescope Images Super-Jupiter
John P. Millis, Ph.D. for redOrbit.com - Your Universe Online
There are several techniques employed by astronomers to discover planets orbiting distant stars. The most popular techniques seek transits - where a planet will pass directly in front of a star, blocking part of its light. Based on the length of the transit, the amount of light that is blocked, and other factors, astronomers can infer a lot of information about the planet.
Additionally, researchers will find planets by observing "wobbles" of stars caused by gravitational forces exerted on the star by the orbiting planets. This is accomplished by observing how the spectral lines of the star shift back and forth over time. Often, teams of astronomers will rely both methods - using multiple instruments - to confirm the presence of the planets.
In both cases, the extrasolar planets are not actually seen directly, but rather inferred by their effects on their host star. The reason being that direct observation is quite difficult. If the planet is too close to its star the light from the raging inferno will overwhelm the weak optical signature of reflected light. Additionally, if the planet is too small, there won't be sufficient light to resolve it. Similarly, if the solar system itself is simply too far from Earth, the signal might be too weak to resolve.
"Imaging provides information about the planet's luminosity, temperature, atmosphere and orbit, but because planets are so faint and so close to their host stars, it's like trying to take a picture of a firefly near a searchlight," explained Masayuki Kuzuhara at the Tokyo Institute of Technology in a recent statement. However, strides are being made in creating new instruments, and refining techniques to begin directly imaging smaller, and smaller worlds.
To this end, astronomers using the Subaru Telescope in Hawaii are now reporting the detection of the smallest extra-solar world using direct detection methods. Known as GJ 504b - so named as it orbits the bright star GJ 504 - the world is several times the mass of Jupiter and with similar size. Such planets are known as Super-Jupiters as it is thought they bare a resemblance to the largest planet of our solar system, but simply on a grander scale.
"If we could travel to this giant planet, we would see a world still glowing from the heat of its formation with a color reminiscent of a dark cherry blossom, a dull magenta," said Michael McElwain, a member of the discovery team at NASA's Goddard Space Flight Center in Greenbelt, Md. "Our near-infrared camera reveals that its color is much more blue than other imaged planets, which may indicate that its atmosphere has fewer clouds."
This landmark discovery is not only important in terms of the technology used to find it, but also because of how it will influence our understanding of solar system formation. The research team has found the planet orbits about nine-times farther away from its host star as Jupiter orbits the Sun. Theoretical models of solar system dynamics struggle to explain how this would be possible.
Leading theories suggest gas giant planets would get their foundational material from gas-reach regions of the planetary nebula - the giant gas cloud that eventually forms the star and the planets that surround it. Collisions between forming asteroids and comets lay the foundations for the planetary cores as well as the gaseous atmospheres.
The problem is the model works well to explain such planets that are close to the star - roughly within the orbit of Neptune in our solar system. But worlds that are farther out, possibly much farther out, do not sit within the model parameters.
"This is among the hardest planets to explain in a traditional planet-formation framework," as Markus Janson, a Hubble postdoctoral fellow at Princeton University in New Jersey, explains. "Its discovery implies that we need to seriously consider alternative formation theories, or perhaps to reassess some of the basic assumptions in the core-accretion theory."
A paper describing the results has been accepted for publication in The Astrophysical Journal and will appear in a future issue.